1.Boil, steam or microwave potato until tender, drain. Cook potato on heated oiled grill plate (or grill or barbecue) until browned both sides.
2.Meanwhile, discard skin and bones from fish, flake flesh into large bowl.
3.To make dressing. Combine juice, oil and mustard in a screw top jar and shake well.,
4.Add potato to large bowl along with onions, capers and dill, toss gently to combine. Divide salad among lettuce leaves.